1. Technical Field
This invention relates to an elastic roll and more particularly to an elastic roll used in a fixing device.
2. Description of the Related Art
In an image forming apparatus using the electrophotography system, such as a copier and a printer, a photosensitive member formed like a drum is uniformly charged and is controlled based on image information. Then, the photosensitive member is exposed to light for forming an electrostatic latent image thereon. The electrostatic latent image is formed into a visible image (toner image) with toner. Furthermore, the toner image is transferred to a recording paper and is fixed by a fixing device. As a result, an image is formed on the recording paper.
The heating/pressurizing-type fixing devices used in the image forming apparatuses are classified into a 2-roll system and a belt nip system. JP Hei. 8-146806 A (corresponding to U.S. Pat. No. 5,546,175) and JP Hei. 11-184300 A (corresponding to U.S. Pat. Nos. 6,029,038 and 6,236,829) disclose the 2-roll system. In the 2-roll system, paper onto which a toner image is transferred passes through a nip portion formed between a fixing roll and an elastic roll, and the toner image is fused to the paper by heating of the fixing paper and pressurizing of two rolls. JP Hei. 8-166734 A (corresponding to U.S. Pat. No. 5,614,999) and JP 2005-173441 A disclose the belt nip system. In the belt nip system, paper is heated and pressurized in a nip portion between a fixing roll and a pressing belt wound on plural rolls, so as to fix a toner image onto the paper.
Most of all, the 2-roll system fixing device for fusing a toner image onto paper by pressurizing with two rolls is high in thermal efficiency, consumes less power, and can fix an image at high speed as compared with fixing devices adopting any other heating fixing system, for example, a hot air fixing system or an oven fixing system. Therefore, hitherto the 2-roll system fixing device has been generally widely used.